Traditionally, polymers in which low modulus, as well as good impact at low temperatures are desired properties, have been prepared from soft poly(vinyl chloride) (PVC). However, because PVC products cause environmental problems due to emissions of chlorinated organic compounds during combustion there is currently a trend towards replacing PVC with other polymers. As an alternative to PVC polymers polypropylene polymers have been employed since such polymers are known to have suitable resistance to heat and chemicals as well as attractive mechanical properties.
WO 98/59002 relates to a heterophasic polypropylene copolymer having a tensile modulus of 420 MPa or less comprising:
i) a semi-crystalline propylene: ethylene and optionally other a-olefin copolymer matrix comprising 0.5 to 10 wt % of ethylene and optionally 5 to 12 wt % of the other alpha-olefin; and
ii) an elastomeric propylene-ethylene and optionally other alpha-olefin copolymer
The amount of component i) ranges from 20 wt % to 90 wt % preferably from 60 wt % to 90 wt % and the xylene soluble fraction ranges from 3 wt % to 30 wt %.
The applicant found that when component i) is a terpolymer a better balancement of tensile modulus and impact properties can be obtained by fine tuning the above composition. In particular an higher tensile modulus can be obtained in addition at higher izod impact properties while maintaining good values of optical properties.